In the front end of manufacturing liquid crystal display (LCD) devices, millions of thin film transistors (TFT), usually formed on a substrate using epitaxial method, control pixels on the displaying structure wherein the substrate can be a glass substrate, a flexible substrate or a silicon substrate. Dark points or luminous points, i.e. defective display pixels, are shown if a portion of the TFT transistors do not function well due to the defects created during the manufacturing process. These defective pixels downgrade the quality of TFT display devices substantially and become an important objective of the TFT transistor testing.
Referred to FIG. 1, it is a diagram of a testing circuit of an LCD in prior art, comprising, formed on a substrate, a plurality of signal paths 11 in parallel and a plurality of gate signal paths 12 in parallel. It further comprises a TFT transistor at the cross point of the signal paths 11 and gate signal paths 12 acting as a control unit of the pixel 131 of the pixel cell 13. The pixel cell 13 usually contains three pixels 131, each corresponding to red (R), green (G), and blue (B) colors, showing colors by mixing these three colors according to an appropriate ratio of the strengths of these primary three colors. Furthermore, testing equipments can test the LCD by coupling probes with testing pads 111 of signal paths 11 and with testing pads 121 of gate signal paths 12.
While testing the characteristics of a specific TFT transistor, it is often to couple the testing pads 111 of signal paths 11 of the specific TFT transistor with a first testing probe of the testing equipment and couple the testing pads 121 of gate signal paths 12 of the specific TFT transistor with a second testing probe of the testing equipment. The testing equipment sends testing signals through the first testing probe, second testing probe, signal paths 11 and gate signal paths 12 into the specific TFT transistor for verifying the characteristics and quality with normal standards.
The testing method mentioned above needs a long testing time because it requires time to move the two testing probes to attach on each pair of specific testing pads 111, 121. Although the time can be reduced by increasing the number of testing probes of the testing equipment, it is still not a practicable method while considering the raising cost.
Referred to FIG. 2, it is a diagram of another testing circuit of an LCD in prior art providing another method to solve the problem occurred in the testing circuit described in FIG. 1 wherein a shorting bar 21 is connected to all of the signal paths 11 and a gate shorting bar 22 is connected to all of the gate signal paths 12. A testing pad 211 connected to one terminal of the shorting bar 21 and a testing pad 221 connected to one terminal of the gate shorting bar 22 are utilized for coupling with the testing probes of the testing equipment. During the testing process, after coupling a first testing probe of the testing equipment with the testing pad 211 of the shorting bar 21 and coupling a second testing probe of the testing equipment with the testing pad 221 of the gate shorting bar 22, the testing equipment sends testing signals by the first testing probe and the second testing probe through the shorting bar 21 and the gate shorting bar 22 into all of the TFT transistors. By driving the TFT transistors on the LCD panel further converts the testing signals to light signals. If there were portions of TFT transistors not being driven successfully result from defects during manufacturing process, the optical inspecting system of the testing equipment can screen them out and save the testing time apparently. The manufacturing process is completed after the shorting bar 21 and the gate shorting bar 22 is further dismembered from signal paths 11 and signal paths 12.
The method mentioned above still can not screen out the defects due to the short defects created during manufacturing process of any two adjacent signal paths among signal paths 11 or signal paths 12. This problem can be solved by dividing the signal paths 11 and gate signal paths 12 into several groups and connecting each group to corresponding shorting bar.
Referred to FIG. 3, it is a diagram of further one testing circuit of an LCD in prior art. The testing circuit in FIG. 3 is usually called 2G2D testing circuit, i.e. 2 gates and 2 drains, for solving the problem not able to inspect the short defects between any two adjacent signal paths among signal paths 11 or signal paths 12. The testing circuit in FIG. 3 comprises a plurality of signal paths 11; a plurality of gate signal paths 12; two shorting bars 31 each connected to odd number signal paths 32 and even number signal paths 33; two gate shorting bars 34 each connected to odd number signal paths 35 and even number signal paths 36. Testing pads 311, 341 for coupling with the testing probes of the equipment are connected to shorting bars 31 and gate shorting bars 34 respectively. While testing, the testing equipment sends testing signals through the shorting bars 31 and the gate shorting bars 34 into preferred portions of TFT transistors by coupling multiple testing probes with corresponding testing pads 311, 341. Within this method, any two adjacent signal paths among signal paths 11 or gate signal paths 12 are connected to different groups of shorting bars, and any short defects between any two adjacent signal paths can be screened out.
There are often short defects between two adjacent signal paths during the manufacturing process of array cells. The testing method in FIG. 3 is an effective way to screen out those short defects between two adjacent signal paths but only suitable for the array testing of LCD devices. During the manufacturing process of liquid crystal cells, color filters are coupled with the substrate and liquid crystal molecules are injected into the substrate. Thus, the testing signals are converted through the liquid crystal cells into light signals and further into light with red, green or blue color corresponding to the three pixels of a liquid crystal cell. Normally, a liquid crystal cell contains three pixels with three primary colors including red, green and blue color and produces images by controlling the light intensities of these three pixels to create desirable colors like purple, yellow, cyan etc. While testing the LCD devices after the step of manufacturing liquid crystal cells, the most effective way for inspecting the LCD devices is to first divide the pixels with color filters into groups according to their primary colors of a liquid crystal cell. The sequential number of the signal paths can be divided into three groups corresponding to three primary colors and thus connected to the corresponding shorting bar.
Referred to FIG. 4, it is a diagram of further another testing circuit of an LCD in prior art. The testing circuit in FIG. 4 is to improve the testing efficiency of liquid crystal cells of LCD devices and is usually called 2G3D testing circuit, i.e. 2 gates and 3 drains, comprising a plurality of signal paths 11 on a substrate; a plurality of signal paths 12 on the substrate; three shorting bars 41 on the substrate wherein each one of the three shorting bars is connected to the (3m+1)th signal path 42, (3m+2)th signal path 43, (3m+3)th  signal path 44 where m is an positive integral number or zero. It is equal to divide the signal paths into three groups and connected to shorting bars 41 wherein the 1, 4, 7, . . . signal path a signal path group 42; the 2, 5, 8, . . . signal path a signal path group 43; and the 3, 6, 9, . . . signal path a signal path group 44. The testing circuit further comprises two gate shorting bars 34 on the substrate wherein each gate shorting bar is connected to odd number gate signal path 35 and even number gate signal path 36. Furthermore, testing pads 411, 341 are connected to one end of the corresponding shorting bars 41 and one end of gate shorting bars 34 for coupling with the testing probes of testing equipments. While testing, testing equipments send testing signals into specific TFT transistors through the shorting bars 41 and gate shorting bars 34 by coupling a plurality of testing probes with a plurality of corresponding testing pads 411, 341. In this testing method, the signal paths 11 are already divided into three groups corresponding to their primary color, and can improve the testing performance by inputting testing signals into specific shorting bars 41 and then inspecting the primary color shown on the specific pixels connected to the specific shorting bars 41. This method is suitable for testing pixels at the step after completing the manufacturing process of liquid crystal cells. However, the disadvantage of this method is that the testing time is obviously increased for including the short defects examination of any two adjacent signal paths 11. The short defects examination of any two adjacent signal paths 11 is to test all possible combinations of any two signal paths selected from the (3m+1)th signal path 42, (3m+2)th signal path 43, and (3m+3)th signal path 44.
As mentioned above, neither of the testing efficiency of array testing or the testing efficiency of liquid crystal cell testing can be improved simultaneously no matter the testing circuit of an LCD in FIG. 3 or the testing circuit of an LCD in FIG. 4 is applied. The testing efficiency of liquid crystal cell testing decreases by applying the testing circuit in FIG. 3, and in the same way the testing efficiency of array testing reduces by applying the testing circuit in FIG. 4. In the rapid progress of LCD industry, the competitive ability includes avoiding the increasing testing time and delaying shipping schedule due to inappropriate testing methods. The competitive ability is further strengthened by providing a solution to solve the testing problems mentioned above.
Therefore, it is an object of the present invention to provide one testing circuit by including additional shorting bars whose number is multiple of the number of pixels in a liquid crystal cell. The problems of the testing efficiency in steps at array testing and at liquid crystal cell testing can be both improved effectively according to the present invention.